Marine vessels provided with vertically arranged revolving cylinders are previously known. A cylinder revolving in the wind will exert pressure at right angles to the wind current. This principle is known as the Magnus law or Magnus effect. Such a cylinder, or rotor, when it is spinning in the wind, generates a low pressure and a high pressure on opposite sides of the cylinder.
As the wind hits a revolving/rotating cylinder from the side, one side of the cylindrical surface naturally goes against the wind, and the other side goes with the wind. There is very little friction on the side that goes with the wind, and much friction on the side that goes against the wind.
On the side that goes against the wind, the velocity of the wind is opposed by the velocity of air adjoining the cylinder, thus retarding the velocity of the wind. This means an increase in pressure. On the other side of the cylinder, the velocity of the wind combines with the velocity of the air layers next to the cylinder, resulting in a decrease of pressure. This leads to a strong force from the increased pressure side to the decreased pressure side, which generates forward thrust in side winds to move the marine vessel.
The above represents a Magnus effect propulsion system, or named after its inventor Dr Anton Flettner, a Flettner rotor.
Such a Flettner rotor does not generate any benefit in head and tail winds. The Flettner rotor generates extra wind resistance as it increases the cross section area of the ship in the wind in sea going operation.